The present invention relates to thin film EL (electroluminescent) devices and to self-luminous devices that can be used as various kinds of light sources for, for example, self-luminous flat panel displays, telecommunications, lighting, and other applications.
In recent years, LCD panels have been widely used for flat panel displays. However, such panels still have several drawbacks such as slow response time and narrow viewing angle. In addition, even in many new systems in which these drawbacks are redressed, there still remain several problems, including unsatisfactory performance and increasing costs in the manufacturing of panels. In these circumstances, thin film EL devices are attracting attention as new light-emitting devices that have excellent visibility because of self-luminosity, high-speed response, and widespread applicability. In particular, organic EL devices, thin film EL devices that use, in all or part of the layers, organic materials, allowing for a simple film-forming step such as vapor deposition or coating at room temperature, have been the focus of much research, as these devices are attractive in terms of manufacturing cost as well as the above-mentioned characteristics.
In thin film EL devices (organic EL devices), the light emission arises from the recombination of electrons and holes injected from electrodes. Research on such devices has long been conducted; however, since the electroluminescent efficiency of these devices was generally low, their practical applications for light emitting devices was still a long way off.
In the meantime, a device was proposed by Tang et al. in 1987 (C. W. Tang and S. A. Vanslyke, Appl. Phys. Lett., 51, 1987, pp. 913.) comprising a hole-injecting electrode (anode), a hole-transporting layer, a luminescent layer, and an electron-injecting electrode (cathode) on a transparent substrate wherein ITO (Indium Tin Oxide) was employed as the anode, a 75-nm-thick layer of diamine derivative as the hole-transporting layer, a 60-nm-thick layer of aluminum quinoline complex as the luminescent layer, and an MgAg alloy having electron-injection properties and stability as the cathode. This device not only made improvement in the cathode but also formed a thin film which had satisfactory transparency even with a film thickness of 75 nm and which was uniform and free from pinholes and the like by employing a diamine derivative, having excellent transparency, for the hole-transporting layer. Thus, because reduction in the device""s total film thickness became possible, light emission having high luminance with relatively low voltages could be achieved. Specifically, with a low voltage of 10 V or less the device achieved a high luminance of 1000 cd/m2 or more and a high efficiency of 1.5 lm/W or higher. This report led by Tang et al. spurned further investigation into improvements in cathodes, suggestions on device constructions, and so forth, and this active investigation has continued to the present.
Thin film EL devices, generally investigated today, are outlined below.
In addition to a thin film EL device, such as one described in the above-mentioned report, having a laminate structure of an anode, a hole-transport layer, a luminescent layer, and a cathode formed on a transparent substrate, a device may comprise a hole-injecting layer formed between an anode and a hole-transport layer, may comprise an electron-transport layer formed between a luminescent layer and a cathode, or may comprise an electron-injecting layer formed between the electron-transport layer and the cathode. Thus, by assigning functions to each individual layer separately, it becomes possible to select suitable materials for each layer, resulting in improvement in device characteristics.
For the transparent substrate, a glass substrate such as Corning 1737 is widely used. A substrate thickness of about 0.7 mm is convenient for use in terms of its strength and weight.
For the anode, a transparent electrode such as an ITO-sputtered film, an electron-beam evaporated film, or an ion-plated film is used. The film thickness is determined by the sheet resistance and visible light transmittance required; however, since thin film EL devices have relatively high operating current densities, in most cases, the film thicknesses are made to be 100 nm or more so as to reduce the sheet resistances.
For the cathode, an alloy of a low work function metal with a low electron injection barrier and a relatively high work function, stable metal, such as an MgAg alloy proposed by Tang et al. or an AlLi alloy, is used.
For the layers sandwiched between the anode and the cathode, many devices have a laminate structure, for example, of a hole-transport layer formed to a thickness of about 80 nm by vacuum vapor deposition of a diamine derivative (Q1-G-Q2 structure) used by Tang et al. such as N,Nxe2x80x2-bis (3-methylphenyl)-N,Nxe2x80x2-diphenylbenzidine (TPD) or N,Nxe2x80x2-bis(xcex1-naphthyl)-N,Nxe2x80x2-diphenylbenzidine (NPD) and a luminescent layer formed to a thickness of about 40 nm by vacuum vapor deposition of an electron-transport luminescent material such as tris(8-quinolinolato) aluminum. In this structure, in order to increase luminance, generally, a luminescent layer is doped with a luminescent dye.
In addition, in view of the general difficulty in obtaining an organic compound having excellent electron-transport properties such as one described above, it has also been suggested that in the luminescent layer/electron-transport layer structure and in the hole-transport layer/luminescent layer/electron-transport layer structure a hole-transport luminescent material be used for the luminescent layer.
For example, Japanese Unexamined Patent Publication No. 2-250292 discloses a device having the hole-transport luminescent layer/electron-transport layer structure that uses, as the hole-transport luminescent material, [4-{2-(naphthalene-1-yl)vinyl}phenyl]bis(4-methoxyphenyl)amine or [4-(2,2-diphenylvinyl)phenyl]bis(4-methoxyphenyl)amine.
International Patent Publication No. WO96/22273 discloses a device having the hole-transport layer/hole-transport luminescent layer/electron-transport layer structure that uses, as the hole-transport luminescent material, 4,4xe2x80x2-bis(2,2-diphenyl-1-vinyl)-1,1xe2x80x2-biphenyl.
At the 1998 MRS Spring Meeting, Symposium G2.1, the hole-injecting layer/hole-transport luminescent layer/hole blocking layer/electron-transport layer structure that uses NPD as the hole-transport luminescent material was disclosed.
Further, Japanese Unexamined Patent Publications No. 10-72580 and No. 11-74079 also disclose various hole-transport luminescent materials.
Thus, using a hole-transport luminescent material as well as an electron-transport luminescent material as the luminescent material allows for the design of a wide range of materials, which in turn provides various luminous colors. However, in terms of electroluminescent efficiency, lifetimes, and so forth, it cannot be said that expectations have been met.
When devices are used in the passive-matrix line-at-a-time scanning displays, in particular, in order to attain a prescribed average luminance, peak luminance needs to be increased to very high levels. This increases the operating voltage, causing the problem of increasing power consumption as a result of power loss or the like caused by wiring resistance. Further, other problems arise, such as an increase in the cost for drive circuits and a decrease in reliability. Furthermore, devices tend to have shorter lifetimes as compared to ones used under conditions of continuous light-emission.
In addition, even with devices having high electroluminescent efficiency and relatively low operating voltages at direct current operation, when the duty ratio increases during operation, the operating voltage required to attain a prescribed average luminance is rapidly increased and also the electroluminescent efficiency itself is reduced as the operating voltage increases.
Moreover, the above-mentioned [4-{2-(naphthalene-1-yl)vinyl}phenyl]bis(4-methoxyphenyl)amine and [4-(2,2-diphenylvinyl)phenyl]bis(4-methoxyphenyl)amine, disclosed in Japanese Unexamined Patent Publication No. 2-250292, have relatively good hole-transport properties and high fluorescent yield. However, since both compounds are low-molecular-weight compounds, they suffer from the problems of low heat-resistance and particularly a short lifetime. In addition, because the compounds require luminescent dye doping, there is a problem concerning manufacturing.
The above-mentioned 4,4xe2x80x2-bis(2,2-diphenyl-1-vinyl)-1,1xe2x80x2-biphenyl, disclosed in International Patent Publication No. WO96/22273, is somewhat superior in terms of heat-resistance as compared to the above-mentioned compounds. However, since the structure of the compound is completely symmetric, the molecules easily become associated with each other, reducing electroluminescent efficiency due to microscopic crystallization and aggregation. Because of this, devices using this kind of compound are unable to obtain satisfactory lifetime when used under conditions of continuous light-emission. In addition, since the compound requires luminescent dye doping, there is a problem concerning manufacturing.
For the above-mentioned Q1-G-Q2 type compound, such as one disclosed in the 1998 MRS Spring Meeting, Symposium G2.1, besides TPD and NPD, the trimers of and the tetramers of triphenylamine have also been reported. As for their heat resistance, it has been reported that they have sufficient levels of heat resistance. However, since these compounds also have high molecular symmetry, the molecules easily become associated with each other, reducing electroluminescent efficiency due to microscopic crystallization and aggregation. Because of this, here also, devices using this kind of compound are unable to obtain satisfactory lifetimes under continuous use. Particularly when the devices are operated at high duty cycles, difficulties arise in achieving satisfactory electroluminescent efficiency and low operating voltages. In addition, since the compounds require luminescent dye doping, there is a problem concerning manufacturing.
Devices using the above-mentioned hole-transport luminescent materials disclosed in Japanese Unexamined Patent Publications No. 10-72580 and No. 11-74079 do not require luminescent dye doping, and thus are advantageous with regard to manufacturing. However, the devices have not yet achieved satisfactory electroluminescent efficiency.
In view of the foregoing and other problems, it is an object of the present invention to provide a thin film EL device that achieves high electroluminescent efficiency, a low operating voltage, and a long lifetime even when the device is operated with direct current or at high duty cycles.
In order to achieve the above-mentioned objects, the present inventors designed materials having various structures and made predictions about more specific properties of the materials by computer simulations. Thereafter, various compounds were actually synthesized and fabricated into thin film EL devices. The inventors then obtained experimental data on the electroluminescent characteristics and lifetimes of the devices for both direct current operation and high duty cycle operation. From an enormous amount of these experimental data, the inventors found that when some specific groups of compounds were used as the luminescent material, the devices characteristically achieved extremely high electroluminescent efficiency, low operating voltages, and exceptionally long lifetimes over a wide range of operating duty cycles, from a direct current to 1/240.
In addition, the molecular orbitals (HOMO and LUMO) of the specific groups of compounds were observed. The results of the observations showed that each individual molecular orbital was localized within a molecule. On the other hand, the hole transporting luminescent materials disclosed in Japanese Unexamined Patent Publications No. 10-72580 and No. 11-74079 were found to have HOMO and LUMO, which are orbitals contributing to luminescent transition, spreading throughout the molecule. From these data and observations, the present inventors found that it is effective in improving in electroluminescent efficiency and so forth when either a hole-transport luminescent material or an electron-transport luminescent material (collectively referred to as xe2x80x9ccharge-transport luminescent materialxe2x80x9d) has at least two molecular orbitals contributing to luminescent transition such that the two orbitals are localized within a molecule and overlap one another. Thus, the present invention was accomplished.
According to one aspect of the present invention there is provided a thin film EL device comprising at least:
a hole-injecting electrode;
an electron-injecting electrode opposed to the hole-injecting electrode; and
a luminescent layer sandwiched between the hole-injecting electrode and the electron-injecting electrode, said luminescent layer containing a charge-transport luminescent material having, within a molecule, a portion contributing to charge transport and a portion contributing to luminescence where at least two molecular orbitals contributing to luminescent transition are localized.
As with the above-mentioned structure, by using a material having a portion contributing to luminescence where at least two molecular orbitals contributing to luminescent transition are localized, because the spatial overlap of the molecular orbitals contributing to luminescent transition is large, the energy of a hole-electron recombination can be utilized more efficiently. Therefore, high electroluminescent efficiency is achieved. Furthermore, since energy utilization efficiency is high, it is also possible to reduce the operating voltage and extend the lifetime.
The term xe2x80x9cportion contributing to charge transportxe2x80x9d is herein defined as a portion which is part of the molecular structure of the charge-transport luminescent material and which contributes to electron transport by hopping. One such example is a tetraphenyl phenylenediamine skeleton.
The term xe2x80x9cportion contributing to luminescencexe2x80x9d is herein defined as a portion which is part of the molecular structure of the charge-transport luminescent material and which includes all molecular orbitals contributing to luminescent transition. One such example is an anthracene skeleton. It should be noted that this is the portion that emits light.
The term xe2x80x9cmolecular orbitals contributing to luminescent transitionxe2x80x9d is herein defined as orbitals that change the status at light emission, and the orbitals include at least two orbitals, HOMO and LUMO. It should be noted that the molecular orbitals can be obtained from a calculation in a conventional manner by using, for example, Chem3D available from CambridgeSoft Corporation, or the MOPAC 97 engine incorporated in WinMOPAC available from Fujitsu Ltd. In addition, each orbital is defined herein to mean, based on the above calculation results, the smallest spatial extent covering 90% or more of the probability of existence of electrons.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that an electron cloud of the portion contributing to charge transport and an electron cloud of the portion contributing to luminescence are localized such that the electron clouds substantially do not overlap each other.
As with the above-mentioned structure, when the electron cloud of the portion contributing to charge transport and the electron cloud of the portion contributing to luminescence are localized such that the electron clouds are substantially separated from each other, the charge transport properties and the luminescent properties can be exhibited individually in different places within a molecule. In addition, quenching due to the interaction between the electron clouds can be suppressed. Consequently, a device is obtained that achieves high electroluminescent efficiency, a low operating voltage, and an extended lifetime.
The term xe2x80x9celectron cloud of the portion contributing to charge transportxe2x80x9d is defined herein to mean the smallest spatial extent covering 90% or more of the probability of existence of all the electrons that are related to charge transport within a molecule.
The xe2x80x9celectron cloud of the portion contributing to luminescencexe2x80x9d is defined herein to mean the smallest spatial extent which spatially includes at least two molecular orbitals selected from the molecular orbitals contributing to the above-mentioned luminescent transition and which covers 90% or more of the probability of existence of all the electrons that are related to luminescence within a molecule.
Specifically, the term xe2x80x9cbeing localized such that the electron clouds substantially do not overlap each otherxe2x80x9d herein includes the case where there is no overlap between electron clouds that are defined by the spatial extent in which the probability of existence of all the electrons is 90% but there is overlap between electron clouds in the spatial extent in which the probability of existence of all the electrons is over 90%. As described above, the electron clouds of each portion being localized such that the electron clouds do not overlap each other are advantageous in exhibiting the function; it should be noted, however, that the case where electron clouds are localized such that the electron clouds do not overlap each other at all is not realistic, and thus such a term is used.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the portion contributing to charge transport and the portion contributing to luminescence are connected by a carbon-carbon bond.
As with the above-mentioned structure, when the portion contributing to luminescence and the portion contributing to charge transport are connected by a carbon-carbon bond, at least two molecular orbitals contributing to luminescent transition are localized without spreading throughout the molecule, and the electron clouds of each portion are localized such that the electron clouds substantially do no overlap each other. Consequently, a device is obtained capable of exhibiting high charge transport and luminescent properties.
The term xe2x80x9cbeing connected by a carbon-carbon bondxe2x80x9d herein includes not only a direct single bond between a carbon atom contained in the portion contributing to luminescence and a carbon atom contained in the portion contributing to charge transport, but also a bond through a divalent group consisting of carbon and hydrogen atoms, such as an alkylene group and an arylene group. For such a divalent group, one having about 1 to 10 carbons is suitable. However, the xe2x80x9ccarbon-carbon bondxe2x80x9d does not include a bond through nitrogen atoms or the like, a direct carbon-carbon double bond, and a direct carbon-carbon triple bond because these may hinder the localization of molecular orbitals.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the charge-transport luminescent material is a compound having an asymmetric and nonplanar molecular structure.
As with the above-mentioned structure, when the molecular structure is asymmetric and nonplanar, amorphous characteristics and non-associating properties are exhibited, and therefore quenching due to the interaction between each of the portions contributing to luminescence of adjacent molecules or the like can be suppressed. As a result, a device is obtained that has high electroluminescent efficiency.
The term xe2x80x9casymmetric and nonplanarxe2x80x9d is defined herein to mean that the molecular structure at its most stable state is not symmetric with respect to a point, a line, or a plane, but is three dimensional.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the portion contributing to luminescence is present within the luminescent layer at 1xc3x971020 to 1xc3x971021 per 1 cm3.
As with the above-mentioned structure, when the portion contributing to luminescence is present within the luminescent layer at a specific density, a device is obtained that achieves high luminance with high electroluminescent efficiency. This can be explained by the fact that when the density of the portion contributing to luminescence is too low, sufficient luminance tends not to be obtained; on the contrary, when the density is too high, quenching occurs due to the interaction between the portions contributing to luminescence, and thus electroluminescent efficiency tends to be degraded.
Here, the number of the portions contributing to luminescence is counted per portion; for example, when the charge-transport luminescent material has two portions contributing to luminescence within a molecule, the number of the portions contributing to luminescence per unit area equals a value that is double the number of molecules per unit area.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the volume ratio of the portion contributing to luminescence is lower than that of the portion contributing to charge transport.
As with the above-mentioned structure, when the volume ratio of the portion contributing to luminescence is lower than that of the portion contributing to charge transport, the possibility of quenching due to the interaction between the portions contributing to luminescence is suppressed. Consequently, a device is obtained that achieves high electroluminescent efficiency.
The term xe2x80x9cvolume ratioxe2x80x9d is herein defined as the ratio of the volume occupied by the portion contributing to luminescence and the like to the total volume of a molecule having the portion contributing to luminescence and the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the portion contributing to charge transport is of a diaryl diphenyl arylenediamine skeleton.
This skeleton is particularly excellent in charge-transport properties, and thus a thin film EL device is obtained that has particularly good electroluminescent efficiency and so forth. Above all, a tetraphenyl phenylenediamine skeleton, such as a tetraphenyl-p-phenylenediamine skeleton and a tetraphenyl-m-phenylenediamine skeleton, is suitable.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the portion contributing to luminescence is an aryl group containing five or more conjugated bonds.
Such an aryl group has high luminance, and thus a thin film EL device is obtained that has advantages of low operating voltages and so forth. Above all, an anthracene skeleton is suitable.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that an electron-donating substituent is directly bonded to the portion contributing to luminescence.
As with the above-mentioned structure, when an electron-donating substituent is directly bonded to the portion contributing to luminescence, the localization of molecular orbitals contributing to luminescent transition is further increased, and thus a device is obtained that achieves higher electroluminescent efficiency.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the charge is a hole.
According to another aspect of the present invention there is provided a thin film EL device comprising at least:
a hole-injecting electrode;
an electron-injecting electrode opposed to the hole-injecting electrode; and
a luminescent layer sandwiched between the hole-injecting electrode and the electron-injecting electrode, the luminescent layer containing a compound represented by the following general formula (1): 
where Ar1 and Ar2 may be the same or different, and each independently represents a substituted or unsubstituted aryl group; Ar3 represents a substituted or unsubstituted arylene group; X represents a substituent containing two or more carbon rings and non-planarly bonding to a diphenylamine portion; and Y represents a substituted or unsubstituted aryl group containing five or more conjugated bonds.
In the above-mentioned compound, the portion contributing to hole transport is of a diaryl diphenyl arylenediamine skeleton and the portion contributing to luminescence includes Y. When a compound having such a molecular structure is used, a device is obtained capable of exhibiting high hole-transport and luminescent properties. Particularly, when the portion contributing to luminescence is Y (excluding substituents when Y is substituted), at least two molecular orbitals contributing to luminescent transition are localized, and an electron cloud of the portion contributing to luminescence and an electron cloud of the portion contributing to hole transport are localized such that the electron clouds substantially do not overlap each other, and thus a superior device is obtained. Consequently, a device using the above-mentioned compound as the hole-transport luminescent material achieves high electroluminescent efficiency, a low operating voltage, and an extended lifetime.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the compound represented by the general formula (1) has a portion contributing to luminescence where at least two molecular orbitals contributing to luminescent transition are localized.
As with the above-mentioned structure, when at least two molecular orbitals contributing to luminescent transition are localized, because the spatial overlap of the molecular orbitals is large, the efficiency of energy utilization of a hole-electron recombination is increased. Thus, a thin film EL device is obtained that achieves high electroluminescent efficiency.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the X in the general formula (1) is a substituent represented by the following general formula (2): 
where R1 and R2 may be the same or different, and each independently represents a hydrogen atom or an alkyl group.
As with the above-mentioned structure, when the X in the general formula (1) is a bulky substituent such as one represented by the general formula (2), this portion becomes twisted and thus the molecules of the hole-transport luminescent material become asymmetric and nonplanar. Thus, molecular association, crystallization, and the like are less likely to occur, resulting in a device achieving high electroluminescent efficiency.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the X in the general formula (1) is a substituent represented by the following general formula (3): 
where R1 and R2 may be the same or different, and each independently represents a hydrogen atom or an alkyl group.
The substituent represented by the above-mentioned general formula (3) is a bulky substituent in which a vinyl group is bonded to a substituent represented by the above-mentioned formula (2). Thus, molecular association, crystallization, and the like are less likely to occur, resulting in a device achieving high electroluminescent efficiency and so forth.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the X in the general formula (1) is a substituent represented by the following general formula (4): 
where R1 and R2 may be the same or different, and each independently represents a hydrogen atom or an alkyl group.
The substituent represented by the above-mentioned general formula (4) is a bulky substituent having nitrogen. Thus, hole-transport properties can be improved and the molecules become asymmetric and nonplanar. Therefore, molecular association, crystallization, and the like are less likely to occur, resulting in a device achieving high electroluminescent efficiency and so forth.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the X in the general formula (1) is a substituent represented by the following general formula (5): 
where R1 and R2 may be the same or different, and each independently represents a hydrogen atom or an alkyl group.
The substituent represented by the above-mentioned general formula (5) is a bulky substituent having a fluorene skeleton. Thus, the molecules become asymmetric and nonplanar, and therefore molecular association, crystallization, and the like are less likely to occur. Consequently, a device is obtained that achieves high electroluminescent efficiency and so forth.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the Y in the general formula (1) is an aryl group substituted with an electron-donating substituent.
As with the above-mentioned structure, when Y is substituted with an electron-donating substituent, the localization of molecular orbitals contributing to luminescent transition is increased, resulting in a device achieving higher electroluminescent efficiency.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the Ar3 in the general formula (1) is a p-phenylene group.
As with the above-mentioned structure, when Ar3 is a p-phenylene group, high electroluminescent efficiency is realized and organic synthesis can be achieved easily, providing a cost advantage.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the Ar3 in the general formula (1) is an m-phenylene group.
As with the above-mentioned structure, when Ar3 is an m-phenylene group, hole-transport properties of the portion contributing to hole transport are improved, resulting in a device achieving high electroluminescent efficiency and a low operating voltage.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (6): 
where R4, R5, R6, and R7 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; and R1, R2, and R3 may be the same or different, and each independently represents a hydrogen atom or an electron-donating substituent.
In the above-mentioned compound, the portion contributing to hole transport is of a tetraphenyl-p-phenylenediamine skeleton and the portion contributing to luminescence is an anthryl group. One phenyl group of diphenylamine is substituted with the above-mentioned anthryl group and the other is substituted with a substituted or unsubstituted 2,2-diphenylvinyl group. Such compound has a portion contributing to luminescence where at least two molecular orbitals contributing to luminescent transition are localized, and an electron cloud of the portion contributing to luminescence and a molecular cloud of the portion contributing to hole transport are localized such that the electron cloud and the molecular cloud do not overlap each other. Further, since a bulky substituent, a 2,2-diphenylvinyl group, is bonded, this portion becomes twisted and thus the molecules become asymmetric and nonplanar. Thus, a thin film EL device is obtained that achieves high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at a wide range of operating conditions, from a direct current to high duty cycles.
A compound represented by the above-mentioned general formula (6) may be (4-{[4-(2,2-diphenylvinyl)phenyl][4-(9-anthryl)phenyl]amino}phenyl)diphenylamine, (4-{[4-(2,2-diphenylvinyl)phenyl][4-(10-methoxy(9-anthryl))phenyl]amino}phenyl)diphenylamine, or the like.
In this patent specification, the names of compounds used herein were named so as to conform to IUPAC nomenclature rules. Specifically, the compounds were named using Chemistry 4-D Draw (available from ChemInnovation Software, Inc.) based on the structural formulae for each compound.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that a compound represented by the following general formula (7) is used as the hole-transport luminescent material: 
where R4, R5, R6, and R7 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; and R1, R2, and R3 may be the same or different, and each independently represents a hydrogen atom or an electron-donating substituent.
The above-mentioned hole-transport luminescent material includes an anthryl group, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport, and further includes a bulky substituent, a substituted or unsubstituted 4,4-diphenylbuta-1,3-dienyl group. Thus, a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (7) may be (4-{[4-(4,4-diphenylbuta-1,3-dienyl)phenyl][4-(9-anthryl)phenyl]amino}phenyl)diphenylamine, (4-{[4-(4,4-diphenylbuta-1,3-dienyl)phenyl][4-(10-methoxy(9-anthryl))phenyl]amino}phenyl)diphenylamine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (8): 
where R4, R5, R6, and R7 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; and R1, R2, and R3 may be the same or different, and each independently represents a hydrogen atom or an electron-donating substituent.
The above-mentioned hole-transport luminescent material includes an anthryl group, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport, and further includes a bulky substituent, a substituted or unsubstituted 2-aza-2-diphenylaminovinyl group. Thus, a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (8) may be [4-({4-[2-aza-2-(diphenylamino)vinyl]phenyl}{4-(9-anthryl)phenyl}amino)phenyl]diphenylamine, [4-({4-[2-aza-2-(diphenylamino)vinyl]phenyl}{4-(10-methoxy(9-anthryl))phenyl}amino)phenyl]diphenylamine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (9): 
where R4, R5, R6, and R7 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; and R1, R2, and R3 may be the same or different, and each independently represents a hydrogen atom or an electron-donating substituent.
The above-mentioned hole-transport luminescent material includes an anthryl group, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport, and further includes a bulky substituent, a substituted or unsubstituted fluorene-9-ylidenmethyl group. Thus, a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (9) may be (4-{[4-(fluorene-9-ylidenmethyl)phenyl][4-(9-anthryl)phenyl]amino}phenyl)diphenylamine, (4-{[4-(fluorene-9-ylidenmethyl)phenyl][4-(10-methoxy(9-anthryl))phenyl]amino}phenyl)diphenylamine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (10): 
where R1, R2, R3, R4, R5, and R6 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; and An represents an arylene group composed of two or more substituted or unsubstituted fused rings.
The above-mentioned hole-transport luminescent material includes an arylene group composed of two or more fused rings, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport. In addition, the material includes two bulky substituents, substituted or unsubstituted 2,2-diphenylvinyl groups. Thus, a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (10) may be [4-({4-[10-(2,2-diphenylvinyl)(9-anthryl)]phenyl}[4-(2,2-diphenylvinyl)phenyl]amino)phenyl]diphenylamine, [4-({4-[10-(2,2-diphenylvinyl)(9-anthryl)]phenyl}{4-(2,2-diphenylvinyl)phenyl}amino)phenyl]bis(4-methoxyphenyl)amine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (11): 
where R1, R2, R7, R8, R9, and R10 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; and An represents an arylene group composed of two or more substituted or unsubstituted fused rings.
The above-mentioned hole-transport luminescent material includes an arylene group composed of two or more fused rings, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport. In addition, the material includes two bulky substituents, substituted or unsubstituted fluorene-9-ylidenmethyl groups. Thus, a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (11) may be [4-({4-[10-(fluorene-9-ylidenmethyl)(9-anthryl)]phenyl}[4-(fluorene-9-ylidenmethyl)phenyl]amino)phenyl]diphenylamine, [4-({4-[10-(fluorene-9-ylidenmethyl)(9-anthryl)]phenyl}[4-(fluorene-9-ylidenmethyl)phenyl]amino)phenyl]bis(4-methoxyphenyl)amine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (12): 
where R1 and R2 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; and An represents an arylene group composed of two or more substituted or unsubstituted fused rings.
The above-mentioned hole-transport luminescent material includes an arylene group composed of two or more fused rings, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport. In addition, the hole-transport luminescent material is substituted with two bulky substituents, substituted or unsubstituted 4,4-diphenylbuta-1,3-dienyl groups. Thus, a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (12) may be [4-({4-[10-(4,4-diphenylbuta-1,3-dienyl)(9-anthryl)]phenyl}[4-(4,4-diphenylbuta-1,3-dienyl)phenyl]amino)phenyl]diphenylamine, [4-({4-[10-(4,4-diphenylbuta-1,3-dienyl)(9-anthryl)]phenyl}{4-(4,4-diphenylbuta-1,3-dienyl)phenyl}amino)phenyl]bis(4-methoxyphenyl)amine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (13): 
where R1 and R2 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group; An1 and An2 may be the same or different, and each independently represents an arylene group composed of two or more substituted or unsubstituted fused rings; and X1 and X2 may be the same or different, and each independently represents a substituted or unsubstituted 2,2-diphenylvinyl group, 4,4-diphenylbuta-1,3-dienyl group, or fluorene-9-ylidenmethyl group or a hydrogen atom.
The above-mentioned hole-transport luminescent material includes two arylene groups composed of two or more fused rings, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport. In addition, the above-mentioned arylene groups are substituted with bulky substituents. Thus, a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (13) may be {4-[bis(4-(9-anthryl)phenyl)amino]phenyl}diphenylamine, [4-(bis{4-[10-(2,2-diphenylvinyl)(9-anthryl)]phenyl}amino)phenyl]diphenylamine, [4-(bis{4-[10-(4,4-diphenylbuta-1,3-dienyl)(9-anthryl)]phenyl}amino)phenyl]diphenylamine, [4-(bis{4-[10-(fluorene-9-ylidenmethyl)(9-anthryl)]phenyl}amino)phenyl]diphenylamine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (14): 
where R4 represents a hydrogen atom, an alkyl group, an alkoxy group, or an aralkyl group; and R1, R2, and R3 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group.
The above-mentioned hole-transport luminescent material includes a terphenyl group, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport. This material also includes a terphenyl group, which is the portion contributing to luminescence, and thus a thin film EL device is obtained that achieves high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (14) may be [4-(diphenylamino)phenyl][4-(4-phenylphenyl)phenyl]phenylamine, [4-{bis(4-methoxyphenyl)amino}phenyl][4-{4-(4-methoxyphenyl)phenyl}phenyl][4-(1-methyl-1-phenylethyl)phenyl]amine, or the like.
According to another aspect of the present invention the above-mentioned thin film EL device may be such that the hole-transport luminescent material is a compound represented by the following general formula (15): 
where R1, R2, R3, and R4 may be the same or different, and each independently represents a hydrogen atom, an alkyl group, or an alkoxy group.
The above-mentioned hole-transport luminescent material includes two terphenyl groups, corresponding to the portion contributing to luminescence, and a tetraphenyl-p-phenylenediamine skeleton, corresponding to the portion contributing to hole transport. This material also includes terphenyl groups, which are the portion contributing to luminescence, and thus a thin film EL device is obtained that achieves particularly high electroluminescent efficiency, a low operating voltage, and an extended lifetime even when the device is operated at various operating conditions.
A compound represented by the above-mentioned general formula (15) may be [4-(diphenylamino)phenyl][bis{4-(4-phenylphenyl)phenyl}]amine, [4-{bis(4-methoxyphenyl)amino}phenyl]bis[4-{4-(4-methoxyphenyl)phenyl}phenyl]amine, or the like.